This is not a dress rehearsal. It’s 10 a.m. in Harlem, an hour when lazy clock- punchers polish off second coffees. But the kids jam ming Democracy Prep Charter School’s halls in crisply pressed uniforms have already digested Shakespeare and Chaucer without benefit of caffeine or whining. Korean language is next. No excuses.

Suddenly, a voice cuts into the clutch of students like a knife.

“Charlie! Over here.”

The voice belongs to Seth Andrew (right), Democracy Prep’s freakishly energetic leader. Charlie has missed two days of class — a whopping 19½ hours of instruction time — to attend Family Court hearings into whether his mom is fit to raise him. I expect sympathy. Charlie gets none.

“If you’re out a day, that’s a big deal,” the headmaster told him. “You were out two days. That’s serious.” Wow.

The mantra here is “no excuses.” It’s brutal. Unreasonable.

And it works.

Because every one of these kids, Charlie included, is headed to college. Schools like this do more than save children. They save the world.

There’s a war on against charter schools. They’re hated by the United Federation of Teachers. And the battle is led by state Sen. Bill Perkins — himself the recipient of a scholarship to an elite private school. Hypocrite.

Today, Perkins holds a hearing designed to wipe out or weaken successful schools like this one that threaten to bring the union to its knees. Democracy Prep, by the way, sits in the middle of his district.

He must be stopped.

I wondered — What makes Democracy Prep so special? The answer is simple: Nothing at all.

With rare care and discipline, every child, in every neighborhood, can be reached. To accomplish this, a charter school has license to break ironclad union rules.

Most of these kids suffer challenges common for a population of overwhelmingly poor minorities. They’re saddled with every stereotype you can throw at them.

Some live in foster care or homeless shelters. One-fourth were in special ed before they got here. One girl spends weekends in prison, bringing schoolwork to show her parents. Another lost four relatives to street violence since September.

Charlie came to Democracy Prep this year reading at a third-grade level. In about six months, he’d improved by two full grades. Remarkable. But not good enough.

“He may be retained in seventh grade a year,” said Andrew.

Like all charters, Democracy Prep, which serves 402 students grades six through nine, is funded by tax money, but is run like a private school. It also gets less money per pupil — $12,500, compared with $16,000 to $18,000 for an ordinary school.

Yet it pays teachers more, has longer days, and students consistently outperform next-door neighbors. Last year, 91 percent of eighth-graders there passed the citywide math test, in a district where just 69 percent passed.

“My son was a super slacker,” said Daniel Clark, the single dad of an eighth-grader, also named Daniel.

“Now, he doesn’t want to leave at night. He wants to be the mayor of the City of New York!” And from the look of Daniel, he’ll do it.

In an age of locked doors and metal detectors, classrooms are wide open, giving it the feel of a suburban campus, though the school is in the thick of West 133rd Street. I spy literature teacher Kimberly Osagie discussing a poem with children so engaged, they don’t notice me.

Perkins’ hostility to charters is as cynical as it is insane. He complains that they siphon off the cream of kids. But these students are chosen by random lottery.

This year, 1,500 kids applied for 81 seats. You have better odds getting into Harvard.

When they drew the numbers, “I cried,” said Katie Duffy, director of external affairs.

We’ll all cry harder if Perkins has his way with charters. Stop him before he kills Harlem.

A Street fight is looming

Is Mayor Bloomberg up for the fight to save our Street?

President Obama didn’t possess the manners to warn our leader that he intended to visit town today to attempt to crush Wall Street. Good Dems have demonized our chief tax-producing industry, turning Wall Street into the embodiment of Elm Street’s Freddy. Our mayor knows better.

This might explain why Bloomberg learned of Obama’s visit like a regular putz. He read about it on blogs. Only then did the president invite him to his address, throwing Bloomberg’s entire day into chaos.

Happy Earth Day, Mr. Mayor. Mud is all that will be left of our town if the prez wrecks the Street.

We’ll see Cam a lot

Cameron Douglas’ fabulous pals, such as BFF Pat Riley, pretty much steered clear of federal court on Tuesday, and avoided watching Michael Douglas’ spawn get his wrist slapped in federal court for dealing drugs. He was handed a five-year sentence.

One who did grace the courtroom was a second-generation demi-celeb, filmmaker Jen Gatien (daughter of tax-dodging former club king Peter). She told me she came to support her pal of a decade. She told a Web site that Cameron had adopted a “family” of addicts to replace his own, and sold drugs only after his folks cut him off. How else was he supposed to support everyone?

I think the court system has yet to see the last of Cameron.

Experts spew nonsense

A network anchorwoman made this solemn claim, as seriously as triple bypass surgery:

“Some experts [where? on Mars?] say the Iceland volcano is an attempt by the Earth to cool itself.”

Now we’ve got “experts” who can read the mind of the — wait for it — Eyjafjallajokull volcano. No mean feat.

If there’s one thing the eruption that has ruined vacations, marred a Polish state funeral, and turned airports from here to Reykjavik into smelly pajama parties has proven, it’s this: Mother Nature is powerful enough to squash us carbon-based mammals from the face of the Earth like fruit flies, if it suits her mood. If she has moods.

Al Gore, you can move to the back of the Gulf Stream. You’re not that important.

Pedro dirty enough for NY

Senate Majority Leader Pedro Espada Jr. is accused of running his health-care business like the Bank of Espada, including ordering $20,000 worth of taxpayer-financed sushi for delivery to the Westchester home where he lives, allegedly, instead of the poor Bronx neighborhood he represents. I’m shocked!

What’s alarming is that Espada keeps getting elected to office and winning jobs of ever-greater responsibility. But this is New York.